The present invention relates to homopolar electric machines, and more particularly, to homopolar electric machines that can achieve greater output voltages at lower rotational speeds.
Homopolar electric machines, also known as Faraday disc machines, were first developed by Michael Faraday in the 19th century. They operate through an effect known as the Lorentz force in which a charged particle moving through a uniform magnetic field encounters a force perpendicular to the movement and magnetic field direction. This force is expressed in the formula,F=q(E+v×B)  (1)where F is the force, q is the charge of the particle, E is the presence of an electric field interacting with the charged particle, v is the velocity of the charged particle, and B is the magnetic field intensity.
In the prior art, the simplest form of homopolar machine is a disk magnet that is rotated about its vertical poles. Electric connections are made through brushes, belts, or liquid metal contacts applied to the periphery and the center axis. When the disk magnet is rotated, a small DC voltage develops across the contacts. This voltage is dependent in part on the speed of rotation. When a load is applied, the current flow is typically large—causing the machine to be classified as a DC current source.
A major limiting factor of prior art homopolar machines has been the low voltage output with high rotational speeds. Although the current output may be large, modern loads seldom require high current at low voltage—with most preferring the opposite. Power electronics can modify the low voltage homopolar output to accommodate such loads; however, this is not a common practice since there exists a plethora of other electric machines that more readily satisfy the load requirements. The disadvantage with most electric machines (and generators in particular) is that their output is directly dependent on the speed of rotation; the faster the rotation, the higher the voltage output. Gear boxes are employed in the art when low RPMs are required. Therefore, there is a need for an apparatus which can leverage the benefits of a homopolar electric machine for operation across a range of RPMs while also developing output voltages normally developed at higher-RPMs.